This invention relates to a circuit interrupter and, more particularly, to a circuit interrupt in which a movable contact arm stopper is provided for determining the OFF position of the movable contact arm.
FIGS. 1 and 2 illustrate one example of a conventional circuit interrupter of the type to which the present invention pertains. FIG. 1 is a sectional side view of the conventional circuit interrupter in the ON position, and FIG. 2 is a partly cut-away side view of the circuit interrupter shown in FIG. 1 in the OFF position.
In these figures, the circuit interrupter comprises an electrically insulating housing 1 composed of a cover 1a and a base 1b on which stationary contact 2 having secured thereon a stationary contact element 2a is fixedly mounted. A frame 3 is also firmly mounted to the base 1b by screws 4 (only one is shown). The frame 3 supports at its projection 3a an operating handle 5 so that the operating handle 5 is rotatable about the projection 3a. The operating handle 5 has mounted thereon a cradle 6 pivotable relative to the operating handle 5.
A toggle link 8, which includes an upper toggle link 8a and a lower toggle link 8b pivotally connected to the upper toggel link 8a by a knee pin 9, is connected to the operating handle 5 by an upper toggle link pin 7 at the upper end of the upper toggle link 8a. The lower end of the lower toggle link 8b is connected by a pin 12 to a movable contact arm 11 which is rotatably mounted on a cross bar 13 on which the movable contact arm 11 is pivotably supported. The cross bar 13 is rotatably supported on the base 1b by a bearing assembly 14 secured by screws 15 on the base 1b. The knee pin 9 of the toggle link 8 is biased toward the operating handle 5 by a tension spring 10 connected between the pin 9 and the handle 5, thus maintaining the upper toggle link 8a in engagement with the projection 7. A movable contact carrier 16 having a movable contact element 16a secured thereon is mounted to the movable contact arm 11. The movable contact carrier 16 is electrically connected to a terminal conductor 17 through a flexible conductor 18.
The circuit interrupter also comprises an electromagnetic trip device including an electromagnetic device 19 which has a movable plunger 19a. A thermally response trip device having a bimetal 20 with an adjusting screw 20a is also provided. In order to pick up the movements of two kinds of trip devices, a trip bar 21 which is rotated by the screw 20a or the plunger 19a is provided. The trip bar 21 is in engagement with a latch 22 which is in engagement with a latch 23 which releasably latches the cradle 6.
The conventional circuit interrupter further comprises a toggle link stopper 25 pivotally mounted on the frame 3 by a pivot pin. The toggle link stopper 25 is limited in its movement by a stopper pin 24 mounted on the frame 3.
When the circuit interrupter is in the ON position shown in FIG. 1, the current flows from the stationary contact 2 to the terminal conductor 17 through a stationary contact element 2a, the movable contact element 16a, the movable contact carrier 16 and the flexible conductor 18. When the operating handle 5 is moved in the direction of an arrow 26, the upper end of the tension spring 10 is moved beyond dead center of the line of action of the spring 10, causing the tension spring 10 to collapse the toggle link 8 to move the movable contact carrier 16 upwards together with the movable contact arm 11 until the operating mechanism takes the position shown in FIG. 2 in which the movable contact carrier 16 is in engagement with the stopper pin 24.
When a very large current flows through the circuit interrupter in the ON position shown in FIG. 1, the electromagnetic trip device is actuated to push out the plunger 19a from the electromagnetic device 19. Alternatively, when an overcurrent flows through the circuit interrupter in the ON position shown in FIG. 1, the thermally responsive trip device is actuated to push the trip bar 21 by the adjusting screw 20a. In either case, the trip bar 21 is rotated to rotate the latch member 22 and then the latch 23 rotates to release the cradle 6 under the action of the spring 10 which biases the cradle 6 to rotate clockwise. The cradle 6 is then rotated clockwise in FIG. 1 so that the toggle link pin 7 moves overcenter causing the toggle link 8 to collapse to rotate the movable contact carrier 16 together with the movable contact arm 11 about the cross bar 13 until they are brought into the TRIP position in which the movable contact element 16a is separated from the stationary contact element 2a.
With the conventional circuit interrupter as above described, when the circuit interrupter is moved into the OFF position, the movable contact carrier 16 collides with the stopper pin 24 mounted on the frame 3. Upon collision, the frame 3 as well as the stopper pin 24 are subjected to a shock and vibration. This vibration of the frame 3 is transmitted to the trip bar 21, the latch member 22 and the latch 23, which often causes disengagement or erroneous unlatching of these elements, resulting in an erroneous tripping of the circuit interrupter. Also, the movable contact carrier 16 can be deformed by any large shock transmitted by the stopper pin 24.